This invention relates to a hemadynamometer suitable for measuring at the user""s wrist such living body information as blood pressure; pulse and so on and, more particularly, to a hemadynamometer having an air bag featured in its structure for oppressing the wrist.
Generally, the hemadynamometer employing an oppression method by means of the air bag is so constituted that the air bag is pressurized to be inflated until the artery is completely closed, thereafter the pressure in the bag is gradually deflated to catch pulsating signals of the artery superposed on oppressing force of the air bag, and the highest, lowest and average blood pressures are discriminated as based on amplitude variation in the signals. There has been known an electronic hemadynamometer for automatically measuring the blood pressure at such body portion for oppression as an arm and a wrist. Generally, in the wrist, there are extending a radius, an ulna, tendons, muscle and two thick arteries called radial artery and ulnar artery which are branched from an upper arm artery. With the wrist-type hemadynamometer employing the oppression by means of the air bag, these two arteries are simultaneously subjected to an ischemia with the air bag inflated, and the blood pressure is discriminated from the pulse signal caught by deflating the air bag.
Since in this case a large oppression force of the air bag is required for the simultaneous ischemia of the two arteries, the user is forced to have a large oppressive sensation. Further, as the ulnar artery is generally present at a deeper position than the radial artery from the surface of the wrist and the pulse signal of the ulnar artery appears earlier than that of the radial artery, and an error is apt to occur in the blood pressure discrimination. It has been attempted, therefore, to attain the ischemia only of either the radial or ulnar artery for the blood pressure discrimination. In Japanese Patent Laid-Open Publication No. 61-11019, for example, a hemadynamometer having an air bag which oppresses only the radial artery has been disclosed, in which the air bag of a shape elongated in the lengthwise direction of the wrist along the radial artery is made not to contact the tendon nor the radius, with a length in the peripheral direction of the wrist made larger than a diameter of the radial artery but smaller than a distance between the tendon and the radius on the palm side of the wrist. Here, as the radial artery extends between the tendon on the palm side of the wrist and the styloid process of radius to be the closest to the surface of the living body at a position adjacent to the styloid process of radius, it becomes possible to have the radial artery subjected to the ischemia under the minimum pressure, by oppressing over a length smaller than the distance between the tendon and the radius and a portion adjacent to the styloid process of radius.
However, the position of the radial artery involves the individual difference, such that the radial artery is not present between the tendon and the styloid process of radius but is running over and outside the styloid process of radius, upon which the radial artery cannot be subjected to the ischemia with the air bag of the type disclosed in the JP Laid-Open Pub. 61-11019. Further, the ulnar artery also runs in general between the tendon on the palm side of the wrist and the styloid process of ulna, but the individual difference shows that there is an event where the radial artery is running outside the styloid process of ulna. Further, since the conventional air bags are kept not to contact the tendon and radius, there have been problems that positional deviation of the air bag is apt to occur as the inflation advances, the artery of which the ischemia is expected is apt to escape within the wrist, and the degree of ischemia is deteriorated.
An object of the present invention is to provide a hemadynamometer which has overcome the forgoing problems of the known devices and is capable of discriminating an accurate blood pressure with a high precision of discrimination, sufficiently in response to the individual difference in the position of the arteries in the wrist, eliminating any positional deviation of the air bag or escaping of the arteries during the pressurizing, reducing any oppressive sensation to the user and thus any burden to the user, and executing the ischemia with such ideal air bag.
According to the present invention, the above object is achieved by providing a hemadynamometer attaining arterial oppression for ischemia with air bag wound on a wrist in its circumferential direction, wherein the air bag is adapted for not oppression of one of two arteries in a wrist of the user which are possibly subject to ischemia but for at least one of oppression and ischemia of only the other artery, with a length of the air bag enough, when the air bag is wound on the wrist from such hard organization area as tendons on palm side as a start point towards the other artery subject to ischemia, for passing over the other artery and reaching at least styloid process of one of two bones at the wrist but not reaching said one of the arteries, and a width enough for locally oppressing the other artery subject to ischemia at a portion substantially right above the styloid process of the bone on the other artery side with respect to lengthwise direction of the wrist.